PAS resins are engineering plastics with good mechanical properties such as heat resistance, flame resistance, stiffness and dimensional stability, and are used in electronic devices and electric devices.
Depending on those applications, however, PAS resins are often required to have additional specific characteristics. For example, when used in cylinder drums in video tape recorders (VTR), they are required to have much higher dimensional stability and good slidability with magnetic tape.
Compositions comprising PAS resins and calcium metasilicate whiskers optionally along with inorganic fillers are known, for example, in Japanese Patent Application Laid-Open Nos. 7-82415, 3-100062 and 59-11359. However, use of those compositions in slide members for parts to be in contact with magnetic tape is unknown.
In order to improve the dimensional stability of PAS resins, it has heretofore been tried to add thereto potassium titanate whiskers, zinc oxide whiskers, aluminium borate whiskers, potassium carbonate whiskers or the like in various technical fields. However, though effective in improving the dimensional stability of the resins in some degree, the addition to the resins of those whiskers is defective in that the whiskers added make the resins thixotropic, often resulting in that the resin compositions containing the whiskers in large quantities are difficult to knead and work. In particular, when the resin compositions are cast into shaped articles, they are often short-shot to give failures. For these reasons, it is inevitable to restrict the amount of the whiskers to be added, and the improvement in the dimensional stability of the resin compositions is naturally limited. In addition, since the resin compositions are hygroscopic, they are still problematic in that the dimensional change in them could not be reduced satisfactorily.
As has been mentioned above, the acceptable amount of the whiskers to be added to the resins is restricted, and the slidability of the resin compositions, which is indispensable when used in members to be in contact with magnetic tape, is poor. Therefore, the conventional, whiskers-containing resin compositions are unsuitable for VTR cylinders (VTR drums).
In order to improve the slidability of drums with magnetic tape, for example, a method has been proposed of adding carbon fibers or carbon beads to the resins for the drums. However, the addition of carbon fibers, especially chopped carbon fibers is defective in that the resultant carbon fibers-containing resin compositions are anisotropic causing the resulting articles made of the compositions lack good roundness, surface smoothness and dimensional stability.
Given that situation, no one has heretofore succeeded in producing good cylinder drums from resins that are substitutable for conventional cylinder drums of aluminium.